1. Field of the Present Invention
The present invention is related to the field of data processing devices and specifically to data processing devices that employ fixed disk storage.
2. History of Related Art
Microprocessor-based data processing systems are composed of several subsystems or major components. Three of these subsystems that have the most affect on system performance are the central processing unit (CPU), the system memory, and the file subsystem. Of these three, however, the fixed disk storage used by the file subsystem has the most significant impact on system performance. The predominance of the fixed disk unit's affect on system response time is due to the presence of electro-mechanical elements in the fixed disk unit. Whereas semiconductor processors and memory have no moving parts and operate at speeds determined by the speed of electrons moving through an impedance element, disk units are characterized by mechanical latencies caused by rotation of the media and/or movement of the head (i.e., seek times). Latencies associated with disk accessed time can be reduced by using a disk cache. Like its cache counterpart in the context of system memory hierarchies, a disk cache is a relatively small, fast, and expensive storage medium into which recently retrieved data from the disk can be stored in anticipation of the data being required in the near future. For disk sectors that are accessed frequently, disk caches can yield significant performance benefits.
Unfortunately, a disk cache can only be useful after it is populated with data. When a system is first powered on or reset, the disk cache is empty. Thus, the great majority of data accesses that occur following a restart can only be fulfilled from the fixed disk. This problem might be acceptable if relatively few disk accesses were needed following restart. In reality however, the system restart of most data processing systems, including all x86-based data processing systems that run a Windows® platform, execute a large number of disk requests following restart. These disk requests are needed to retrieve portions of increasingly complex operating systems from disk and store them into memory. Files on disks are typically allocated sequentially when they are installed. When accessed (data files) or executed (program files), it is relatively rare that an entire file is used. During a boot sequence, for example, large portions of software such as the operating system's help files are not accessed. In addition, during boot sequencing, a reference to an entity in one file frequently invokes another file that may reside on a portion of the disk storage that is physically distant from the calling program. For at least these reasons, the boot sequence is characterized by frequent accesses to disk storage where there is substantially no relationship between the data requested in each access. In contexts other than system boot sequencing, it may be common to detect a disk access sequence that is repetitive. In such cases, it would be desirable if the repeated nature of the requests could be recognized by creating an entirely sequential (contiguous) copy of the requested data and a mapping from the original data sequence of the relocated data sequence such that, during a subsequent access to this data, the requested data would lie in a contiguous portion of the disk.